1. Field of Invention
Various exemplary embodiments of the present invention relate to an electronic device and, more particularly, to a memory system, a semiconductor memory device and methods of operating the memory system and the semiconductor memory device.
2. Description of Related Art
A semiconductor memory device may be classified into a volatile memory device and a nonvolatile memory device.
The volatile memory device typically performs high speed data read and write operations, but the stored data is lost when the power is cut off. The non-volatile memory device operates at relatively lower write and read speeds, but the stored data is preserved even when the power is cut off. Therefore, the non-volatile memory device is used to store data that is to be maintained regardless of power supply. Examples of the non-volatile memory device include a read only memory (ROM) device, a programmable ROM (PROM) device, an electrically programmable ROM (EPROM) device, an electrically erasable and programmable ROM (EEPROM) device, a flash memory device, a phase-change RAM (PRAM) device, a magnetic RAM (MRAM) device, a resistive RAM (RRAM) device, a ferroelectric RAM (FRAM) device, or the like. The Flash memory device may be typically divided into a NOR device and a NAND device.
The flash memory device enjoys the advantages of both RAM and ROM devices. For example, the flash memory device may be freely programmed and erased similar to the RAM device. Similar to the ROM device, the flash memory device may retain the stored data even when it is not powered. The flash memory device has been widely used as the storage media of portable electronic devices such as mobile phones, digital cameras, personal digital assistants (PDAs), and MP3 players.
Recently, as the number of bits of data stored in a single memory cell of a semiconductor memory device has increased, the time taken for a read operation of the semiconductor memory device may be increased.
Therefore, a need arises for an efficient read operation of the semiconductor memory device.